Only handle CE default styles that have rule sets

Some CE default styles might not have RuleSets, this CL adds some
null checks.

Bug: 895512

Change-Id: I02e0f5070c36c72e8d03ed950d96783506f05c5a
Reviewed-on: https://chromium-review.googlesource.com/c/1343585
Commit-Queue: Rakina Zata Amni <rakina@chromium.org>
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609990}
2 files changed